The present invention relates to certain novel chemical compounds. These compounds are useful as precursors for the chemical vapor deposition of thin films, thermochromic materials, conductive polymers, light-emitting diodes, and molecular charge-transfer salts.
Chemical vapor deposition is a process where thin films of elements are deposited on substrates by using volatile precursors. The precursors are heated to high temperatures, usually over 1000.degree. C., where they vaporize and release a desired element on a substrate. The disadvantage with conventional precursors is that they must be heated to extremely high temperatures. Another disadvantage with conventional precursors is that they deposit unwanted elements on the substrate in addition to depositing the desired element.
An article by Sandor Karady et al. entitled 1,2,5-Thiadiazole-1-Oxides. I. Synthesis and Reactions of Alkoxy and Alkythio Analogs,- in Heterocycles, Vol. 16, No. 9, pp. 1561-1568, (1981), discloses a compound of the formula: ##STR1## where E'=S, X=nothing or O, and R alkoxy, S-R, aminoalkyl, or aminoaryl.
An article by V. Bertini et al., entitled 1,2,5-Telluradiazole, C.sub.2 H.sub.2 Te in Acta Crystallography, C40, pp. 653-655, (1984), discloses a similar compound to that disclosed by Karady et al. This compound is a compound of formula A where E'=Te, X=nothing, and R=H.
A similar compound is also disclosed in an article by Tristram Chivers et al., entitled Preparation, Crystal Structures, and Isomerization of the Telurium Diimide Dimers RNTe(.mu.NR').sub.2 TeNR(R-R'-.sup.t Bu; R=PPh.sub.2 NSiMe.sub.3, R'=.sup.t Bu, .sup.t Oct): X-ray Structure of the Telluradiazole Dimer [.sup.t Bu.sub.2 CH.sub.2 N.sub.2 Te].sub.2, in Inorganic Chemistry, Vol. 35, No. 1, pp. 9-15, (1996). This compound has the structure of formula A where E'=Te, X=nothing, and R=a fused conjugated ring.
In addition, a compound of formula A is disclosed in an article by Herbert W. Roesky et al., entitled Cyclisation of Bis(2,2,2-trifluoroethoxy)-1,2-diiminoethane with Sulfur, Selenium, Phosphorus, and Arsenic Chlorides, in Z. Naturforsch., pp. 1315-1318 For this compound, R=trifluoroethoxy, and X=Cl when E'=P or As; X=nothing when E'=Se; and X=O or nothing when E'=S.
Still further, an article by H. Buchwald et al., entitled Synthese Und Reaktionen Von 1,2-Bis(trimethylsilyl)iminen 2, in Journal of Organomnetallic Chemistry, Vol. 166, pp. 25-30, (1979), discloses a compound of formula A, where R=aryl, and E'=C(sp.sup.2) when X=O; E'=S when X=nothing or O; E'=Se when X=nothing; and E'=P when X=O and phenyl on the same molecule. This article also discloses a compound of formula B, shown below, which can be used to make compound A. The compound of formula B has the following structure: ##STR2## where Y=SiMe.sub.3 or H, and R=aryl.
Similar to the compounds disclosed by Buchwald, an article by von Gerdy Tuchtenhagen et al., entitled Darstellung und Reaktionen von 1.2-Bis-trimethylsilyliminen, in Liebigs Ann. Chem., Vol 711, pp. 174-183, (1968), also discloses a compound of formula A, which can be made from a compound of formula B. For the compound of formula A, R=aryl, and E'=S when X=nothing or O, and E'=C(sp.sup.2) when X=O. For the compound of formula B, Y=SiMe.sub.3 or H, and R=aryl. The disadvantage of the compounds of formula B disclosed by Buchwald and Tuchtenhagen, if used as precursors to form other compounds, is that they are not especially reactive because the aryl groups on these molecules only act as weak electron withdrawing groups and because the aryl groups cannot be further functionalized (substituted) readily.
Still further, the Benzildiimine References found in SciFinder, Aug. 11, 1998, pp. 1-3, disclose a compound of formula A where R=phenyl, and X=nothing when E'=Se; and X=2 chlorine substituents when E'=Te.
Many of the compounds discussed above are generally unsuited for use in chemical vapor deposition and other processes for several reasons. The disadvantage of some of the compounds of formula A disclosed by Karady, Bertini, Chivers, Roesky, Buchwald, Tuchtenhagen, and SciFinder is that E'=S, Te, Se, all elements that have limited bonding capabilities. It is not as desirable to use these precursors with Group VI elements for chemical vapor deposition because they are only able to bond with 2 compounds, and thus, X must be nothing. In addition, using such compounds to create light emitting diodes is problematic because these compounds do not have substituents that extend the conjugation of the system. Still further, the chemistry of these Group VI elements cannot necessarily be applied to elements that bond with 3 or more elements. Another disadvantage with some of the compounds of formula A disclosed by the articles discussed above, such as that disclosed by Karady, Roesky, Buchwald, Tuchtenhagen, and SciFinder, is that X is Cl or O. The disadvantage with these compounds is that when E' is deposited on a substrate, Cl or O tend to be deposited too. Both of these elements cause contamination of the film being deposited. Still further, when X=Cl, the electronic properties of the compound are altered. Furthermore, Cl and O limit the ability of the compound to further functionalize and therefore are not desirable substituents for enabling these compounds to be used as light emitting diodes. Still further, when X=Cl, the compound is moisture sensitive and decomposes via hydrolysis.
In addition, an article by Manfred Weidenbruch et al., entitled 1,3,2-Diazasiloles by Silylene Addition to Trifluoracetonitrile [1], in Z. anaorg. allg. Chem., Vol 622, pp. 1811-1813, (1996), discloses a compound of formula A where E'=Si, X=2 alkyl substituents, and R=CF.sub.3. The method for making this compound involves generation (photochemical) and reaction of a silylene (R.sub.2 Si:) species, and thus, it is unique to making compounds where E'=Si. Thus, the method disclosed does not suggest how other compounds having E' as another element could be formed.
Several articles by Arthur Ashe and others disclose multi-step low yield reactions for producing compounds similar to that of the compound of formula A except that both nitrogens are replaced by carbons, which may have substituents thereon. For these compounds disclosed by Ashe, E'=Sb, As or Bi and R=H or alkyl. These articles are Aromatic Antimony Compounds, Transition Metal Complexes of 2,5-Dimethylstibacyclopentadienyl, by Arthur Ashe et al. in Journal of Organometallic Chemistry, Vol. 202, pp. C95-C98, (1980); Synthesis of 2,2',5,5'-Tetramethylbibismole. A Thermochromic Dibismuthine, by Arthur Ashe et al. in Organometallics, Vol 3, pp. 495-496, (1984); Synthesis and Molecular and Crystal Structure of 2,2',5,5'-Tetramethylbiarsolyl, by Arthur Ashe et al. in Organometallics, Vol. 2, pp. 1005-1008, (1983); and 2,2',5,5'-Tetramethyldistibolyl. A Thermochromic Distibine, by Arthur Ashe et al. in Journal of American Chemistry Society, Vol 103, pp. 207-209, (1981). These articles further disclose that this compound may be used as a thermochromic material.
An article by P. O'Brien et al., entitled Precursor Chemistry: Remaining Challenges and Some Novel Approaches, in Journal of Crystal Growth, Vol 170, pp. 23-29 (1997), discloses a compound similar to the compounds disclosed by Arthur Ashe, where both nitrogens in the compound of formula A are replaced by carbons, which may have substituents thereon. This article suggests that these compounds can be used in chemical vapor deposition. The disadvantage with the compounds disclosed by Ashe and O'Brien is that thin films formed using these compounds have carbon contamination because carbon atoms are directly attached to the element E' being deposited on a substrate.
Methods have also been devised for depositing multiple elements on a substrate. The most common approach for chemical vapor deposition of multi-element materials is to use two or more precursors that react individually on the incipient film. The traditional classes of compounds used for the chemical vapor deposition of multi-element thin films involve the reaction of a Group III (B, Al, Ga, In) alkyl with a Group V (N, P, As, Sb, Bi) hydride, alkyl, or alkyl amino compound. One problem with forming these multi-element films with conventional precursors is that the precursors containing the different elements typically differ greatly in their reactivities. This makes it difficult to control the stoichiometry of the film formed. Frequently, the differences in reactivity are countered by using large excesses of the more recalcitrant precursor(s). Still further, these precursors are typically exceedingly pyrophoric and toxic. Thus, when large excesses of a recalcitrant precursor are used, the process creates large amounts of waste that may be toxic.
To overcome the deficiencies found with conventional compounds, a number of novel chemical compounds, methods for making these novel chemical compounds, and applications for using these compounds are needed in the art. More specifically, compounds that may be used as precursors for chemical vapor deposition of thin films are needed. Still further, compounds that can deliver multiple elements in the chemical vapor deposition of thin films are also needed. Still further, compounds that may be used as thermochromic materials, conductive polymers, light-emitting diode precursors, and molecular charge-transfer salt precursors are also needed.